<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <div>
    <input type="text" id="ipt">
    <button id="btn">按钮</button>
  </div>

  <script>
    // master 内容
    var ipt = document.getElementById('ipt')
    var btn = document.getElementById('btn')
    btn.onclick = function () {
      alert(ipt.value)
    }
  </script>
</body>

</html>